The object of the present invention is to provide organic pigments with enhanced pigment properties that are useful for the coloration of high-molecular-weight organic materials.
The present invention relates to the general discovery that pigment compositions containing a substantially transparent filler having particles of a specified particle size and particle size distribution show enhanced pigment properties in specific applications, such as the coloration of plastics or surface coatings, especially paints or printing inks.
Inorganic fillers are used in large quantities by the pigments industry for various purposes. For example, flaky micas, mainly with a particle size in the range from 10 to 30 .mu.m, covered with a thin layer of a metal oxide, such as TiO.sub.2, are used as a substrate for the preparation of pearlescent pigments. Due to their large particle size, these effect pigments are directly incorporated in automotive paint systems without a dispersion step, as stir-in pigments. However, paints containing such effect pigments usually have a clear coat layer above the pigmented base coat which improves the gloss by covering surface defects and/or unevenness caused by the large particles of the effect pigments.
For example, DE 4211560 discloses composite pigments wherein a mica is coated with various inorganic pigments. The reference broadly suggests that various fillers and pigments, including organic pigments, can be combined to form coated particles having the same geometry as the filler.
The fillers in the inventive pigment compositions are not generally coated by the organic pigment. Instead, the inventive pigment compositions are physical mixtures wherein the filler is, for the most part, not coated with the organic pigment. Thus, when the inventive pigment compositions are dispersed, an electronmicrograph shows that the filler and organic pigment are present as distinct components of the composition. The inventive pigment compositions perform well as pigments for plastics to be used in extrusion and molding processes, as stir-in pigments for coating compositions, in laser marking applications and for ultraviolet (UV) or electron-beam (EB) cured ink systems.